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T. Copley

Testing Detergents: Establishing Efficient Methods for Formulation, QC and Comparative Assessment

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Understanding Test Requirements

Laundry detergents are complex formulations incorporating a range of functional ingredients that may include: surfactants; buf-fers; chelating agents; enzymes; polymers; fragrances and opti-cal brighteners. Their physical form has evolved from traditional powders through powder tablets, to liquid detergents and cap-sules, and the commercial marketplace is highly competitive, with consumers sensitive to both performance and price. Understand-ing the relative benefit of incorporating what can be expensive ingredients is crucial in formulation/product development, while exemplary QC is essential for long term market advantage.When it comes to assessing product performance there are a number of factors to consider. The issue of stain removal is clearly paramount with a range of different soils routinely tackled – from wine, chocolate and fruit juice through to oil/grease, mud and blood. Effective cleaning relies in the first instance on removal of the soil from the fabric but preventing re-deposition is vital. Enzymes are used routinely to enhance soil breakdown, particularly for biological stains and for low temperature washing, while cellulosic/polymeric ingredients are often incorporated specifically to inhibit re-deposition [1].

Other characteristics that directly impact consumer opinion, and consequently product value, include the ability of the de-tergent to:

• Maintain whiteness – with optical brightening and fluores-cent whitening agents (OBAs/FWAs respectively) often used to enhance perceived whiteness.

• Maintain colour – with many products now sold on their ability to reduce colour fading.

• Inhibit dye transfer – since this enables a broader range of clothing to be washed together.

Test requirements for textile manufacturers are closely aligned. Colour maintenance and dye transfer inhibition (fastness) are the primary issues but there are also certain special consider-ations for specific textiles. For example, fabrics for swimming apparel are routinely tested for their ability to withstand ex-posure to hypochlorite (chlorinated water).

Testing Detergents: Establishing Efficient Methods for Formulation, QC and Comparative Assessment T. Copley*

abstract

Detergents are ubiquitous within our homes with increasingly sophisticated formulations cleaning our clothes, crockery and cutlery to exacting standards, in a wide array of domestic appliances. The effective removal of different types of soiling is

essential but it is also critical to maintain the integrity of the item being washed. Reducing the environmental burden of routine cleaning is an ongoing target and drives trends towards enhanced performance at lower wash temperatures, and the use of more environmentally benign ingredients. Detergent re-formulation is an ongoing, continuous activity.To support formulation, for QC and for comparative performance testing, detergent manufacturers require relevant, reproduc-ible, cost-efficient tests that can be applied easily in the laboratory. For laundry products this need extends to textile manufactur-ers, since the maintenance of colour and integrity in the face of successive washes is intrinsically associated with higher quality fabrics. Ultimately, the performance and impact of detergents is assessed under real-life conditions using a domestic appliance, but this is time consuming, costly and has a number of other limitations, with respect to routine use within the lab. The Tergotometer was introduced in the 1950s specifically for laundry detergent testing within the laboratory and the core design remains in widespread use today; a testament to its relevance and value. In the intervening decades, this design has been refined to exemplary efficiency, and adapted to deliver an effective set-up for dishwasher detergent testing. In tandem, testing strategies have evolved considerably, not least as a result of the introduction of associated international standards. With a modern Tergotometer, built to exacting specifications, and a rigorously considered test protocol, even closely similar, high performance detergents can be reliably differentiated in a highly energy and water efficient manner. In this article we examine the requirements for detergent testing, the factors that influence results and the application of the Tergotometer for both laundry and dishwashing products, highlighting its benefits relative to alternative techniques. The pri-mary aim is to provide the understanding and background information required to instigate effective laboratory testing based on modern equipment and strategies so as to cost efficiently generate data to support product development and manufacture.

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The market for dishwashing powders, liquids, gels and tablets is equally competitive and formulations are just as complex, drawing on a range of ingredients with similar functionality including: complexing agents; surfactants; bleaching compo-nents; enzymes and wetting agents. However, the focus of testing is slightly different with soil removal, the avoidance of re-deposition, and the resulting finish (clarity and shine) the key characteristics assessed. Detailed evaluation of the effect of a detergent on crockery and cutlery (for example, corro-sion, loss of gloss, cloudiness) is typically more of an issue for those charged with specifying appropriate washing instruc-tions for any given product. The range of soils encountered is arguably less diverse but presents an equally tough challenge with requirements for oil/grease based soil removal, for exam-ple, quite different from those most suitable for the removal of proteinaceous deposits.

Establishing a Testing Strategy

For all detergents there is a need for test methods that are practical, reliable, reproducible and sufficiently differentiating to detect superior performance and/or any failure to meet a specification. Ensuring that testing meets these goals calls for careful consideration and control of the factors that can impact the results obtained. These can be broadly classified under the headings: test equipment; test conditions and ma-terials; analytical techniques and assessment criteria.

Test Equipment

The most representative way to test a detergent, in terms of customer experience, is in a full-scale domestic appliance, and ultimately all detergents are tested this way. However, for screening and QC this approach has some important limitations. Firstly, the equipment required takes up a large amount of lab-space, is noisy, energy consuming and requires a large amount of test materials, water and detergents. Typi-cal washing cycles are around 60-90 minutes for laundry and 120 minutes for dishwashing, so such tests are also lengthy, leading to a low analytical throughput. Furthermore, there is limited opportunity to closely control test conditions and the potential for ‘carryover’ of soil or detergent, from one test to another is a recognised issue. The need for alternative, lab-scale instrumentation has long been recognised, with the Launderometer one of the first systems introduced for laundry detergent testing. This instru-ment has enjoyed widespread use and enables some control of test conditions. However, the washing action applied is far from representative of that of a domestic washing machine, the equipment required is space-consuming, and test times are still relatively long [2], in the order of 20 to 40 minutes. The Tergotometer directly addresses these issues and is a sim-pler solution that enables more rapid, representative testing. It consists of a number of miniature washing machines (eight in modern instrumentation) in a single bench top instrument

(see Fig. 1). Each test station comprises a glass test vessel, usually 1000mL in size, and an agitator. The test stations are held in a water bath, for precise temperature control, with the samples clearly visible during washing (unlike with the Laun-derometer). Temperature, agitator speed and cycle time can all be controlled to apply the conditions required, and testing is typically complete in around 15–20 minutes (for a laundry detergent). An important development of the Tergotometer has been the introduction of an accessory that enables it to be used for testing dishwasher detergents; test cycles for these products are even shorter – in the order of 10 to 15 minutes (discussed later).In summary, testing with a Tergotometer boosts analytical throughput in laundry detergent testing by around three to eight times compared with using a standard domestic appli-ance, and compared with alternative laboratory instruments such as the Launderometer, at the same time enabling re-producible testing under closely controlled conditions. It is therefore extremely useful for generating the statistically significant data needed to justify claims of performance im-provement. Other routine applications include:

• Washability and colour fastness testing

• The optimisation of washing conditions for specific detergents (e.g. temperature and water hardness)

• Assessment of brightening, softening and foaming

Test Conditions and Materials

A primary consideration with respect to test materials is the source of the soil: ”real life” or laboratory produced. In the USA, for example, ASTM D2960 [3] specifies the use of “real life” soils for home laundering products. However, the use of ”real life” soils does not easily facilitate the development of direct links between specific formulation ingredients and the

Fig. 1 A Tergotometer set up for routine laundry testing with op-tional refrigeration unit installed for operation between 10 °C and 70 °C. (Source: Copley Brochure)

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removal of certain stains, or indeed other aspects of deter-gent performance, or offer the level of control that can be achieved using laboratory produced soils. For screening, for-mulation and QC it can therefore be preferable to use labora-tory produced stains, as specified in ASTM D3050 and ASTM D4008 [4,5].Traditionally, laboratory produced stains were manufactured and applied in-house – a messy and time-consuming process with poor reproducibility. Over recent decades, companies specialising in the supply of laundry samples with closely de-fined stains, pre-applied to a suitable substrate, have become well-established and it is now possible to purchase samples in a range of fabrics, sizes, and volumes, for many different stains. Samples are also available in a range of colours, includ-ing white, to test colour maintenance and fastness. Stain samples for dishwasher detergent testing are equally accessible, typically ‘baked on’ to melamine tiles (to mimic the performance of porcelain), though other substrates such as glass or stainless steel may be usefully deployed. Since the choice of samples directly impacts the measured wash profile, recommendations by groups such as that established by Ger-man Industrial Association of the Manufacturers of Toiletries and Detergents (IKW) can be helpful in determining an opti-mal set [6]. Testing with an established collection of stains is extremely helpful when comparing the performance of differ-ent dishwasher detergents with closely similar performance.Beyond the issue of soil there are a number of test conditions that can impact the results obtained. These include:

• The ratio of detergent to water – detergent concentration

• Temperature

• Water hardness and pH

• Washing time

• Rinsing time

• Washing action

• The load (especially when testing within a domestic appliance)

The development of a robust testing strategy therefore calls for definition with respect to all of these variables in order to optimise repeatability and reproducibility.

Assessment

Following testing, a comparative assessment of samples is carried out to determine the effectiveness of the washing process; this can be either manual – by eye – or carried out using a spectrophotometer or colorimeter.Manual inspections for textiles typically take the form of visu-al comparison to an appropriate Grey Scale, to either assess colour change or staining. These scales consist of five pairs of grey (colour change) or grey and white (staining) chips as

detailed in ISO 105-A02 and A03, respectively [7,8]. Amer-ican Association of Textile Chemists and Colorists (AATCC) Evaluation Procedures 1 and 2 similarly cover this aspect of testing [9,10]. Alternatively laundered materials may be grad-ed by experienced evaluators under closely controlled condi-tions, under incandescent light and daylight, for example, as detailed in ASTM D2960 [3]. In either case, such assessments can be somewhat subjective, even where steps are taken to make them as robust as possible.Instruments for direct, quantitative assessment include col-orimeters which translate colour information into tristimulus values yielding results akin to the human eye and the more sophisticated spectrophotometers, which provide wave-length-by-wavelength spectral analysis to produce precise data beyond that observable by the human eye. Colorimeters are ideal for straightforward colour measurement and ideally suited for the determination of colour difference and fast-ness as well as routine comparisons of similar colours. Their relatively simple and robust construction makes the colorim-eter the ideal tool for QC operations. The spectrophotome-ter is a far more accurate instrument designed to measure the precise colour in the human visible light wavelengths as well as infra red and UV ranges. This sophistication makes it optimal for both high precision quality control and research and development applications. The spectrophotometer may include a calibrated amount of UV in the light source, which can be important when it comes to assessing the impact of OBAs/FWAs. Portable, easy to use and readily calibrated for specific applications, colorimeters and spectrophotometers can also be implemented in automated systems, complete with robotics, to streamline testing and reduce the manual input required, and are suitable for evaluating the results of both laundry and dishwasher detergent tests. ASTM D3050 [4] provides details of how to manipulate reflectance mea-surements to generate a soil removal index (SRI) to assess the cleaning capability of laundry detergents (see equation).

%SR = [(Rw – Ru)/(Rn – Ru)]*100

Where: %SR = % stain removal; R = reflectance, n = normal unstained unwashed fabric, u = stained unwashed fabric, and w = stained washed fabric.

Re-deposition can be quantified using the re-deposition index (RI) which is defined as [11]:

RI =RA/RB * 100

RA = average reflectance of unsoiled cloth after completion of the testRB = average reflectance of unsoiled cloth before testing

Reflectance measurements may also be used to quantify the whiteness of a sample using a variety of equations such as CIE whiteness and yellowness of textiles via similar indices or

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b* scales, positive (yellow) to negative (blue), for yellowness from the CIE L*a*b* colour space. The use of a colorimeter brings precision to performance assessment but steps should be taken to maximise the repeatability such as, measuring samples in a consistent orientation [4]

Testing with a Tergotometer: Procedures and PracticalitiesTo illustrate the practical implications of current understand-ing and standards it is worth looking in a little more detail at a typical laboratory based procedure, using a Tergotometer, for a laundry detergent, and for a dishwasher detergent.

Laundry Detergent TestingFig. 2 shows a Tergotometer set up for routine laundry test-ing; operation is simple. Firstly the water bath temperature is adjusted to give the test temperature required, and then 1000mL of water (adjusted to a suitable hardness) is added to each vessel. Once the system has equilibrated at the re-quired temperature (adjustable between ambient and 70 °C or between 10 °C and 70 °C with optional refrigeration unit), detergent is added, agitation ensuring its homogeneous dis-persion within the water. Fabric test samples are then dropped into each test station as loose swatches and ‘washed’ at a specified agitator speed (between 50 and 200 rpm) for a defined period of time. Each test station accepts up to 12, 5 cm x 5 cm or 6, 8 cm x 8 cm swatches. A wide range of standardised pre-soiled test fab-rics of suitable dimensions are now widely available from spe-cialist suppliers of detergent testing materials (please consult with the author for details).Once washing is complete the samples are removed from the vessels, wrung out, and rinsed in fresh water, for a defined period of time. This washing and rinsing cycle may be repeat-ed, as required.All test swatches are assessed, both before and after washing/drying (and ironing if necessary) and it is common practice to use an equal number of test and clean fabrics so that stain removal efficiency and re-deposition can be assessed in a single test.

Triplicate testing is common place to safeguard the statistical significance of the results.

Dishwasher Detergent TestingDishwasher detergents can be tested in an exactly analogous way using the accessory shown in Fig. 3, which is added to the conventional paddle in each Tergotometer vessel [12]. This accessory holds six pre-stained sample tiles (7.5 cm x 2.5 cm) mounted at angles close to the side of the test vessel. The tiles are available from several specialist companies in various materials, melamine (to simulate porcelain), glass, stainless steel, etc. and are pre-stained to customer selection; Shep-herd’s Pie, Spaghetti Bolognese, Creme Brulee, and Egg Yolk for example. The coated/stained tiles are placed such that no two adja-cent tiles have the same soil to improve test relevance. Water volume and temperature, detergent concentration, agitator speed and test time are controlled, as with laundry detergent testing, and a rinsing cycle is similarly applied. The tiles are then removed for drying and analysis, typically by spectro-photometry.

In Conclusion

The performance of detergents is ultimately assessed using full-scale domestic appliances but for formulation and QC, this is a time-, energy- and product-consuming approach that can be less than optimal in terms of the data generat-ed. Identifying and applying laboratory techniques that offer standardised, relevant, highly reproducible testing can sub-stantially reduce analytical costs and at the same time deliver more useful data. The Tergotometer is a laboratory instru-ment developed specifically to meet requirements for labora-tory detergent testing. Over five decades its design has been refined to the point of precision performance and a recently released accessory has extended application to dishwash-er detergents. Today’s Tergotometers can help all detergent

Fig. 2 Test Station for Laundry Detergents with and without stan-dardised pre-soiled fabric swatches. (Source: Copley Scientific)

A B

Fig. 3 Test Station for Dishwasher Detergents prior to and during the test. (Source: Copley Scientific)

A B

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[6] ‘Method for ascertaining the cleaning performance of dishwasher detergents’

SOFW Journal, 125. Jahrgang 11 / 99

[7] ISO 105-A02 1993 (BS EN 20105-A02 1995): Textiles – Test for colour fastness

– Part A02: Grey scale for assessing change in colour

[8] ISO 105-A03 1993 (BS EN 20105-A03 1995): Textiles – Test for colour fastness

– Part A02: Grey scale for assessing

staining

[9] AATCC Evaluation Procedure 1

‘Gray Scale for Colour Change’.

[10] AATCC Evaluation Procedure 2

‘Gray Scale for Staining’

[11] ‘Terg-O-Tometer testing’ JOACS Vol

66, No 1 (Jan 1989)

[12] Leenerts, L.O. ‘Soil Removal by Dish-

washing Detergents’ JAOCS Vol 33,

March 1956.

testing

manufacturers (and indirectly the manufacturers of textiles re-liant upon them for washing) to fully optimise and streamline their testing strategies and access the data required in the most cost- efficient way.

References

[1] Binder, D ‘Laundry Detergent Chemistry’ online presentation, available for

viewing at http: / / www.slideserve.com / colum / laundry-detergent-chemistry,

April 2006

[2] Harris, J.C. ‘Detergency Evaluation. III. Adjustment of Terg-O-Tometer and

Launderometer Wash Test Methods to Produce Comparable Soil Removal Data

[3] American Society for Testing Materials (ASTM) D2960-05: Controlled Launder-

ing Test Using Naturally Soiled Fabrics and Household Appliances.

[4] ASTM D3050 – 07: Measuring Soil Removal from Artificially Soiled Fabrics (Not

Suitable for Detergent Ranking).

[5] ASTM D4008 – 95 (reapproved 2009) Measuring Anti-Soil Deposition Proper-

ties of Laundry Detergents (Not Suitable for Detergent Ranking).

*contact

Tony Copley

Copley Scientific LimitedColwick Quays Business Park,

Private Road No. 2, Colwick, Nottingham, UK, NG4 2JY

Tel: +44 115 961 6229 Fax: +44 115 961 7637

www.copleyscientific.com